The present invention relates to a method for producing a catalytic converter and heat exchanger used in an exhaust gas cleaning-up system for an internal combustion engine or the like, and a member to be used in the method, more particularly to the method for assembling a ceramic honeycomb structure wound with a low-friction supporting member into a metallic can while compressing the supporting member, and to the supporting member of low friction for the honeycomb structure when producing the catalytic converter and heat exchanger.
Various methods have been proposed to assemble a ceramic honeycomb structure, which is vulnerable to mechanical shocks, into a metallic protective structure. One of the common methods is the so-called clamshell method, in which a pair of symmetric half shell whose form is mutually symmetrical is welded to each other to contain a ceramic structure. Another method is rolling, in which a ceramic honeycomb structure is wound with a supporting member and further with a metallic plate forming a cylinder, and the overlapping ends of the plate are welded to each other, to form a protective structure. Still another method is intrusion, in which a honeycomb structure is intruded together with a supporting member into a cylindrical, metallic protective structure.
Each of these methods, however, has its own disadvantages. The clamshell method involves, for example, a durability-related problem. Density of the supporting member tends to decrease in the vicinity of the welding line of the clamshell, because of the limitation set by the welding. This lower-density section will be attacked more notably by the exhaust gases than are the other sections of the supporting member and hence deteriorated more, with the result that it may not be able to absorb mechanical shocks sufficiently, possibly leading to damages of the honeycomb structure while in service, including sudden destruction, and preventing it from exhibiting its inherent functions. Wind erosion originating from the welded section is another problem involved in this method.
Rolling may not be highly suitable for industrial purposes, because it needs more welding labor than the clamshell method.
Intrusion is superior to the above two methods in that it needs no welding work. A mat of ceramic fibers as the supporting member is put into a metallic can by the aid of a dedicated jig, because of large friction between the mat and can. At present, however, it is difficult for this method to put the supporting member into the can sufficiently uniformly in density to make the honeycomb structure it protects resistant to repeated attacks by the exhaust gases, when they are in service in a catalytic converter.
For example, production of a catalytic converter of an intruded honeycomb structure, disclosed by Japanese Patent Application Laid-Open No. 7-77036, needs a retainer ring to prevent misalignment of the honeycomb axes, because a mat as the supporting member alone is difficult to support the honeycomb structure uniformly at a high surface pressure, which evolves when the mat is highly compressed to increase friction resistance.
However, use of a retainer ring to prevent axial misalignment partially closes the honeycomb ends, causing partial loss of performance of the exhaust gas cleaning-up system. The adverse effect it causes is similar to that resulting from projection of the mat from a honeycomb end.
It is therefore highly demanded to develop an intrusion method which allows a honeycomb structure to be held by a mat alone at a sufficient surface pressure to support them, without needing a device, such as retainer ring, to prevent axial misalignment of the honeycombs.